Fierce global competition over fossil fuels is driving the process industries to rethink the way their businesses will operate in the future. U.S. manufacturers will have to develop strategies to conserve energy.
The Energy Information Administration reported in 2005 that the process industries accounted for about 80% of the total energy consumed in the U.S. industrial sector. This percentage is similar to one presented in a 1991 report by the Department of Energy. Sixty-four percent of the energy consumed in a process plant today is used by electric motors; energy is the second largest expense after feedstock. In the very near future, energy conservation will have more of an effect on economic success than in the past. Your operation could well depend on how successful you are at reducing energy consumption. (For more details on energy management, see the Energy Saver column.)
By integrating smart motor control centers (MCCs) that will monitor energy consumption a plant can remove wasteful energy expenditure, prevent unplanned downtime, and improve overall operational efficiency. Recent tax code amendments make these improvements inviting.
A closer look
Distributed control systems (DCSs) were designed to provide regulatory control. They were based on proprietary components such as operating systems, networks, hardware and configuration tools. In a typical DCS, communication was slow and methodical, carried out within a circumscribed system boundary using discrete and analog signals. Programmable Logic Controllers (PLCs) were designed for high-speed control of discrete devices like motors, pumps, and drives.
In the traditional process plant, PLCs managed the electrical infrastructure such as motors, drives and MCCs, while regulatory control was left to the DCS. Only critical motor performance data was passed along to the plant’s DCS because of the cost of field wiring. It was virtually impossible to determine the energy consumption for individual processes within a business unit. Plants were limited in their ability to schedule partial shutdowns to improve energy efficiency or reduce energy consumption during peak demand.
Today, a new class of DCS has emerged that can integrate and control high-speed discrete devices like MCCs, drives, soft starters, breakers and power metering devices. These new DCS’ enable dynamic monitoring of motor performance, offering the potential for a leap forward in improving energy management and operational efficiency.
The integration of motor management data directly into the DCS allows the device to communicate its operational condition and status. This can be used for real-time monitoring of motors to detect motor problems before they occur. Maintenance is no longer reactive. Predictive and preventative measures can now be performed to prevent motor failure and damage, allowing plant operators to extend the life of their motors. Because motors consume the majority of the energy in the plant, monitoring the operating condition is an essential aspect of any energy conservation and maintenance program.
Up to 40% of a plant budget goes to maintenance. As much as 60% of scheduled maintenance checks on valves and motors prove unnecessary. The largest cost associated with this support is maintenance labor, which is wasted on false alarms. A secondary cost, often unnoticed, is fatigue and having these people unavailable when you need them. Monitoring motor operations can help plant management develop an effective predictive and preventative maintenance program focused on maximizing operational efficiency.
Over the past two decades, significant improvements have been made to increase motor efficiencies above industry averages. Electric motors consume 10 to 25 times their purchase price in electricity each year, so even a 1% increase in motor efficiency can mean thousands of dollars worth of savings in the operation of the motor. Premium efficiency motors cost a little more because of the superior material that goes into them, but the higher cost typically can be recovered in 12 months or less. Implementing a plant-wide replacement strategy — as motors burn out — can significantly reduce your electrical bill over time.
Variable frequency drives (VFDs) are a popular approach for matching electrical draw to actual need. VFDs are often superior to the traditional choice: a fixed-speed motor plus regulatory control valve. By regulating the speed of a drive to directly control flow rate, a 50% energy reduction can often be achieved in fluid flow control applications.
The motor control center
Motor control systems have a prominent role in industrial processes. These systems are often housed in an MCC that contains a comprehensive array of control and monitoring devices. Advances in technology and decreased cost of electronic devices have led to a boom in the inclusion of various controls and monitoring devices into the MCC. These devices, like relays, VFDs, and soft starters, are capable of providing a wealth of data back to the control system regarding the condition of the motor. This information can be presented in the DCS in a clear and easy-to-read format that can be used to increase productivity, minimize downtime and energy consumption, and improve personnel safety. Figure 1 shows the network view of a typical smart MCC. Each combination motor control unit is called a motor bucket. A bucket is an integral part of an MCC.